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Don't compute the Kronecker symbol in ec_GFp_simple_set_compressed_coordinates.

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If y is zero, there is no point with odd y, so the odd bit may not be
set, hence EC_R_INVALID_COMPRESSION_BIT. This code instead computed the
Kronecker symbol of x and changed the error code to
EC_R_INVALID_COMPRESSED_POINT if not a square.

As the comment says, this was (intended to be) unreachable. But it
seems x was a typo for tmp1. It dates to before upstream's
6fb60a84dd1ec81953917e0444dab50186617432, when BN_mod_sqrt gave
garbage if its input was not square. Now it emits BN_R_NOT_A_SQUARE.
Upstream's 48fe4d6233ac2d60745742a27f820dd88bc6689d then mapped
BN_R_NOT_A_SQUARE to EC_R_INVALID_COMPRESSED_POINT.

Change-Id: Id9e02fa1c154b61cc0c3a768c9cfe6bd9674c378
Reviewed-on: https://boringssl-review.googlesource.com/12463
Reviewed-by: Adam Langley <agl@google.com>
This commit is contained in:
David Benjamin 2016-11-25 14:43:22 -05:00 committed by Adam Langley
parent bd691756f2
commit 14ebb4ff27
1 changed files with 1 additions and 13 deletions
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14
crypto/ec/oct.c
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@ -381,19 +381,7 @@ int ec_GFp_simple_set_compressed_coordinates(const EC_GROUP *group,
if (y_bit != BN_is_odd(y)) { if (y_bit != BN_is_odd(y)) {
if (BN_is_zero(y)) { if (BN_is_zero(y)) {
int kron; OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSION_BIT);
kron = BN_kronecker(x, &group->field, ctx);
if (kron == -2) {
goto err;
}
if (kron == 1) {
OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSION_BIT);
} else {
/* BN_mod_sqrt() should have cought this error (not a square) */
OPENSSL_PUT_ERROR(EC, EC_R_INVALID_COMPRESSED_POINT);
}
goto err; goto err;
} }
if (!BN_usub(y, &group->field, y)) { if (!BN_usub(y, &group->field, y)) {